Pythonisation

[a-slide]

Here are a few suggestions to pythonise the package:

• Raise an explicit exception when a wrong argument in the dict is passed to "Browser" or "load_track"
• Check that local files passed are readable (os.access(fp, os.R_OK))
• Docstring are better, but a description of the args would help when people want to know more about the functions (displayed with shift+tab in jupyter)

Thanks